Virtual Machines

The virtual machine (VM) is a classic concept inhardware virtualization and is usually used to provide virtual environments to cater for software needs. Numerous software solutions enable the operation of several guest systems on a common host system. But how do virtual machines work, and what advantages and disadvantages are associated with this virtualization concept? We’ll introduce you to the basics of hypervisor-based hardware virtualization and show you step by step how to deploy virtual environments for Windows or Linux.

In hardware virtualization, physical system resources can be distributed across multiple virtual systems. Each guest system (including all programs running in it) is separated from the underlying hardware.

In practice, virtual machines are mostly used to isolate certain processes and applications for security reasons. Compared to other virtualization concepts, VMs offer a strong encapsulation, functioning as a basis for hosting products in which several customer servers are operated on a common hardware platform. The provision of virtual machines is the basis of shared hosting and VPS (virtual private server) setups. Since each guest system runs in an isolated runtime environment, processes encapsulated in a VM do not affect the host system or other systems on the same physical machine.

In a business context, virtual machines are used to reduce costs for operating and maintaining IT infrastructures. Companies often run an extensive IT infrastructure that is idle most of the day. Virtual machines can significantly reduce this wastage. Instead of providing each application area of a business IT department with its own physical machine, more and more companies are moving to running mail, database, file, or application servers in isolated virtual environments on the same powerful hardware platform. This concept is implemented in the context of server consolidation, as it is usually cheaper to maintain a large computing platform for different virtual systems than to operate several small computers. Processors, in particular, are still expensive to buy. In other words: unused processor time is an unnecessary cost factor that can be avoided by switching to virtual systems.

Another field of application for virtual environments is software development. Programmers who develop applications for different system architectures often use virtual machines for software testing. Numerous hypervisor products allow the parallel operation of different operating systems or system versions. Virtual machines can be created, cloned, and removed from the physical hard disk space at the touch of a button without leaving any data behind. In addition, faulty processes within a virtual machine have no effect on the underlying system due to encapsulation.

Home users typically use hypervisors with emulation capabilities to run applications originally written for a different system architecture. However, it should be noted that hardware virtualization, as well as emulation, always goes hand in hand with performance losses. For example, if a user wants to run a Linux program in a VM on their Windows machine, additional resources must be spent on both the hypervisor and the guest system. An encapsulated Linux application like this no longer has the same performance of the underlying hardware at its disposal. This is referred to as an overhead.

Hardware virtualization is reaching its limits, especially for resource-intensive workloads. If multiple virtual machines are running on the same host system, the resource requirements of one machine during performance peaks can also affect the performance of the other machines on the same host. This can be counteracted by guaranteeing each virtual machine a fixed contingent of hardware resources. Make sure that the total of all virtual resources used simultaneously never exceeds the maximum available power of the physical machine.

The following table compares the main advantages and disadvantages of virtual machines. To what extent these benefits and limitations matter depends primarily on the framework within which you want to deploy VMs and the purpose of virtualization.

The following step-by-step instructions will show you how to create a virtual machine on a Windows host and run it as a guest system in this Ubuntu Linux. For the tutorial we use Windows 7 and Oracle VM VirtualBox as hypervisor software.

Various software solutions are available to create a virtual operating system. Market leaders are products from Oracle, VMware, and Parallels.

The following table shows the most popular hypervisor products for Windows, Linux, and macOS as well as possible guest systems.

For the following tutorial we used the hypervisor VM VirtualBox from Oracle. The software is available free of charge to users under the GNU General Public License (GNU GPLv2). We recommend downloading from the vendor’s website. To do this, proceed as follows:

1. Access http://www.oracle.com/technetwork/server-storage/virtualbox/downloads/index.html
2. Select the current download package for your operating system (in our example, Windows)
3. Save the .exe file with the binary data in any directory on your computer

To run a guest system in a virtual machine, you need an operating system image. This is a memory image that can be interpreted by the hypervisor software as a system hard disk. This can be in the open file format .iso. Common virtualization solutions also use proprietary container formats for image files such as .vdmk (VMware), .vhd (Xen and Microsoft Hyper-V) and .vdi (Oracle VM VirtualBox).

For this tutorial, we are using the open source operating system Ubuntu 17.10.1, which can be downloaded as an .ido file from the official Ubuntu project website. To do this, proceed as follows:

1. Access https://www.ubuntu.com/download/desktop
2. Select the current version of the operating system and click on “Download”
3. Save the .iso file locally on your system

In the next step, decide whether you want to create a new virtual disk or assign an existing virtual desk to the virtual machine.

In this tutorial, we will create a new virtual hard disk on which to reinstall the guest system from scratch.

Select the option “Create a virtual hard disk now” and confirm your selection by clicking on “Create.”

Confirm your selection with “Next.”

The next step is to decide whether you want to allocate a fixed amount of available disk space to the virtual machine. Alternatively, you can dynamically allocate space on the physical disk. In this case, no fixed contingent is assigned to the VM; instead, the memory resources used on the physical hard disk automatically adjust to the VM memory requirements.

The newly created VM appears with your chosen name in the list of available virtual machines.

VM VirtualBox creates a file folder for each virtual machine. This is automatically created in the storage designation you selected and contains the VDI file for the virtual hard disk, a log file, and a definition of the VM.

We select the .iso file with the Ubuntu 17.10.1 memory image.

All changes that you make in your VM are automatically written to the VDI file that you created as a virtual hard disk during configuration. If you want to run the guest system on another computer, simply copy the file folder on your virtual machine (including VDI file, log file, and definition) to the corresponding device. Note that each machine that you want to run your VM on must have compatible virtualization software.

An alternative to providing guest systems in virtual machines is container-technology. We’ll explain to you how applications can be virtualized using containers at the operating system level and what kind of advantages this type of virtualization brings in our beginner tutorial for the docker container platform.